MUSK and myasthenia gravis: Classification of MG subgroups is as follows: early-onset MG (AChR), late-onset MG (AChR), thymoma MG (AChR), MuSK MG, LRP4 MG, seronegative MG (no autoantibodies detected) and ocular MG (AChR, MuSK, LRP4 or none).